A fuel assembly comprises fuel rods arrayed in a square lattice pattern of 10 rows and 10 columns, and three large-diameter water rods arranged along a diagonal line of the fuel assembly in such a region as able to accommodate 10 fuel rods. Partial length fuel rods are arranged in an

A second fuel rod positioned at each corner of a channel box and second fuel rods adjacent to the former are formed to have a smaller outer diameter than that of ordinary first fuel rods, so that a pitch between the second fuel rods is narrower than a pitch between the first fuel rods.

A fuel assembly comprising a plurality of fuel rods, where fuel rods containing a burnable poison element having a smaller neutron absorption cross-section such as boron are provided in a region of soft neutron energy spectrum and a large thermal neutron flux and fuel rods containing

In a fuel loading method for a reactor core made up by high burn-up fuel, fuel assemblies loaded in a circumferential zone of the core are shuffled between two layers of the circumferential zone until residing in the core for two cycles and, after residing for two cycles, are moved to th

The present invention provides a structural component for constituting a reactor core comprising one and the other metallic members arranged adjacent to each other in a reactor, and reduction means for reducing a difference in the swelling between the metallic members due to neutron

In a fast breeder reactor provided with a core comprising a core region packed with a fissile material and a blanket region which surrounds the outside of said core region and most of which is formed of a fertile material, and a plurality of control rods which are put in and out of the

In a nuclear reactor, gaps are defined between fuel assemblies so that moderators can be inserted. Hence, the nuclear characteristics vary between the central portion and periphery of the fuel assembly so that the local output peaking becomes greater on the periphery of the fuel asse